1. Field of the Invention
The present invention relates to resist imaging, particularly to color resist imaging useful in prepress color proofing.
2. Background of the Art
In many forms of color imaging, it is necessary to use more than one color to provide a final color rendition of an image. In the area of printing technology, most images are produced from cyan, magenta, yellow and black images which are laid down in sequence and in register. These four colors (or only cyan, yellow, and magenta) can be combined to provide the effect of most visible colors.
In laying down the images of these three or four colors, not only do the individual color images have to contain the proper color densities, but the separate images must be in register with each other in order for the correct image to appear in the reproduction. Both in printing and in color prepress proofing, marks are placed on the receptor sheet outside of the field of the printing to assist in placing the different color images into register. These marks are known in the trade as registration marks. By having the marks in the identical portion of the field to be imaged (but outside the field of the desired image), each successive color image can be placed in good registration with the previous images. Each registration mark is printed in the same color as the overall color of the individually printed color layer; that is, the registration mark for the cyan layer is cyan, for the yellow layer it is yellow, and for the magenta layer it is magenta. The color must be the same as the registration mark is printed at the same time and with the same imaging material (e.g., ink or transferred mass) as is the major portion of the image.
Most images are placed onto a white or near white (e.g., bone or ivory) receptor sheet such as paper. The registration marks for the cyan and magenta layers are quite readily visible on a white background, but yellow does not readily provide a clearly visible contrast against a white background. This poorly contrasting yellow image will not provide a good registration mark because it cannot be readily seen by the printer. If the mark cannot be clearly seen, it becomes difficult to place any successive images in register with the yellow image. It is not reasonable to place a different color on the area of the registration mark as this would probably have to be done manually on each image.
A technique must be developed for providing better contrasting registration marks on printed or proofing yellow registration marks.